Excavation machines, for example hydraulic excavators, dragline excavators, wheel loaders, and front shovels, operate according to well known cycles to excavate and load material. A typical cycle includes a dig segment, a swing-to-truck segment, a dump segment, and a swing-to-trench segment. During each of these segments, the excavation machine performs differently. For example, during a dig segment, high forces and high precision are required to push a tool into the material at an optimum attack angle, while during a swing-to-truck or swing-to-trench segment, high velocities and low precision are required. As such, the excavation machine is often controlled differently according to what segment of the cycle is currently being completed. In addition, the way in which the machine is controlled during each segment can affect productivity of the machine, and the way that productivity is measured and analyzed.
A common way to measure productivity is to monitor the payload excavated and transported by the machine during each individual work cycle. Payload monitoring can be performed by way of pressure sensors or load cells associated with actuators and/or linkages that connect a tool of the excavation machine to a frame thereof. Based on the measured pressures or forces and on machine calibration, the weight of the material within the tool can be determined.
Although somewhat affective, measuring payload with pressure sensors or load cells can be difficult when the tool is moving. That is, the work cycle is typically not interrupted to perform the payload monitoring. As such, the payload must be monitored at the same time the tool is moving to complete the work cycle. When monitoring the tool during an active work cycle, care should be taken to minimize measurement error caused by movement of the tool (i.e., caused by changes in the velocity and/or acceleration of the tool). In addition, care should be taken to ensure that the dig segment of the work cycle is complete (i.e., filling of the tool for that particular work cycle is complete) and that the dump segment has not yet been initiated (i.e., no material has been intentionally lost prior to the monitoring).
One payload monitoring system that may be used during an active work cycle is disclosed in U.S. Pat. No. 5,714,719 (the '719 patent) issued to Otsuka et al. on Feb. 3, 1988. The '719 patent discloses a workload detecting system for excavating and loading apparatus. The workload detecting system includes a bottom pressure sensor detecting system for detecting a bottom pressure of a cylinder that vertically pivots a bucket, and a bucket earth and sand amount calculating system for calculating an earth and sand weight within the bucket on the basis of the detected bottom pressure. The bottom pressure sensor detecting system continuously measures the bottom pressure and calculates an average value of pressures monitored from 0.1 seconds before to 0.1 seconds after a time Td. The time Td corresponds with a predetermined period of time (e.g., 2 seconds) ahead of a timing when a bucket dump signal is input. Then, on the basis of the averaged pressure, the bucket earth and sand amount calculating system calculates the bucket earth and sand weight by referencing a map stored in memory. By calculating the weight based on an average of pressures measured just before dumping occurs, the calculation may have high accuracy.
Although the system of the '719 patent may calculate payload at a generally reliable time during a typical work cycle to avoid negative influences, accuracy of the calculation could be improved. That is, the best time during the work cycle to calculate payload may not always be the same. Specifically, based on operator control, movement over uneven terrain, environmental conditions, and other uncontrollable factors, the window during which the most accurate measurements can be taken may shift. By limiting the measurements to a fixed time during each cycle, some of the measurements may lack accuracy. In addition, the system of the '719 patent fails to accommodate movement of the tool during the measurement time period.
The disclosed system is directed to overcoming one or more of the problems set forth above.